EASA AD 2026-0128
Engine Fuel & Control – Hydromechanical Metering Unit – Replacement
Summary
EASA Airworthiness Directive 2026-0128 is an official safety directive addressing the replacement of Hydromechanical Metering Units (HMUs) on SAFRAN Helicopter Engines ARRIUS 1A models, commonly installed on Airbus Helicopters AS 355 N twin-engine helicopters. The directive targets specific HMUs identified by part number 01648511170 and certain serial numbers listed in the AD. It mandates the replacement of affected HMUs to prevent engine fuel flow issues that could lead to uncommanded engine shutdowns.
What Changed
This new Airworthiness Directive introduces mandatory replacement requirements for affected HMUs due to identified defects in the constant delta P valve diaphragm. It prohibits the installation of these affected HMUs on any engine after the effective date and provides detailed compliance timelines based on engine usage cycles. The directive also allows for a single ferry flight without passengers to perform the replacement if necessary before the next flight.
Why It Matters
This directive is critical for aviation professionals as it addresses a safety risk that could cause uncommanded engine shutdowns, potentially compromising helicopter control. Operators and maintenance organizations must ensure compliance to maintain airworthiness and avoid operational disruptions. Compliance teams need to track affected HMUs and adhere to the specified replacement schedules to meet regulatory requirements and ensure flight safety.
What To Do
Operators must identify engines with affected HMUs and replace at least one HMU within the specified compliance times based on accumulated cycles, with full replacement required subsequently. No affected HMU may be installed on any engine after 09 July 2026. If immediate replacement is required, a single ferry flight without passengers is permitted to reach a maintenance facility. Compliance deadlines vary from immediate replacement before next flight to within 24 months depending on engine usage.
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